WO05/028550 discloses functional polymers which have a first, surface-active segment and a second, functional segment which generates the desired properties of the functional polymer. These functional polymers are blended with nonmodified thermoplastic bulk polymers, and the resulting blends are used to produce moldings or similar articles or to produce coatings, in order to exert targeted control over the properties of the surfaces of the articles or coatings obtained. The surface-active modification of individual film-forming constituents of a coating composition which is crosslinked only after application to give a coating having targeted surface properties is not, however, described in WO05/028550.
Furthermore, the functional polymers described in WO05/028550 are employed for biological or medical applications, such as for cosmetics, for the biocidal treatment of gloves, clothing, medical instruments, and the like, or for the biocidal finishing of air filters and the like, and also for the production of diagnostic chips, by bioactive surface treatment of the chips.
The descriptions do include descriptions of alkoxysilane-functional, surface-active moldings and coatings where the bulk polymers are treated in some cases with polymeric additives which have alkoxysilane groups. The curing of the alkoxysilane groups in those cases is by a number of hours of moisture treatment or by treatment with aqueous acids. This treatment, which is typical in the field of plastics parts, is associated with considerable additional cost and inconvenience in the field of automotive finishing, however, and is therefore undesirable. Moreover, clearcoat materials that are typically employed in the field of automotive finishing are generally incompatible with the aqueous acids required, meaning that it is not possible to transpose the functional coatings described in WO05/028550 to the field of automotive finishing.
Furthermore, the as yet unpublished American patent application with the Ser. No. 11/227,867, of Sep. 15, 2005, describes coating compositions which comprise reaction products (I) of a dimer fatty acid diol with an isocyanatoalkyltrialkoxysilane.
A particular feature of the coatings obtained using these coating compositions is a very high gloss. As the fraction of the reaction products (I) of a dimer fatty acid diol with an isocyanatoalkyltrialkoxysilane in the coating compositions goes up, the hardness and the resistance to solvents, as measured in double rubs with methyl ethyl ketone, goes down. In the field of automotive finishing, however, the demand is increasingly for coatings having an improved hardness and resistance and hence an improved scratch resistance.
EP-B-1 295 914, furthermore, discloses coating compositions featuring an enhanced oil and water repellency effect, these compositions comprising an alkoxysilyl-functional acrylic resin, an acrylic resin containing alkoxysilyl groups and secondary dimethylpolysiloxane chains, a hydroxyl- and epoxy-functional acrylic resin, and a polyester resin having a high acid number. On account of the relatively broad molecular weight distribution of the poly(meth)acrylates with alkoxysilane groups, however, solids contents of less than 50% by weight only are generally realizable in the clearcoat materials. At higher proportions, the coating materials are difficult to process, on account of their high viscosity. On curing, moreover, unwanted Si—O—C nodes may form in competition with the desired Si—O—Si nodes, as a result of transesterification of the —Si(O-alkyl)3 groups with ester units of the adjacent alkyl (meth)acrylate comonomer units, the Si—O—C nodes being hydrolytically labile and leading to reduced chemical resistance on the part of the resulting coating. Since the heavy-duty OEM clearcoats are to have as a high a weathering resistance as possible, it is a concern that, as compared with polyurethane networks, the poly(meth)acrylate networks exhibit a reduced weathering resistance.
That patent, however, describes neither a difference in degree of crosslinking of the coating in the near-surface layer and in the bulk, nor the control of the properties of the coating by means of these differences in the degree of crosslinking.
EP-B-1 204 701 describes coating compositions which as well as nanoparticles comprise a surface-active substance, whereby an accumulation of the nanoparticles at the surface comes about in the coating, leading to improved scratch resistance on the part of the coatings. The extent of such structures is usually low, similar to a chain of beads on the surface.
Owing to the extremely strong interparticulate interactions and to the usually incomplete stabilization of the particles, however, there are frequent instances of particle agglomeration and hence an adverse effect on the leveling and the appearance of the resulting coatings. Furthermore, extremely effective stabilization of the particles is necessary in order to ensure a wide processing window and to avoid possible deposits in the circuit lines. The last-mentioned publication also fails to describe either a difference in degree of crosslinking of the coating in near-surface layer and in the bulk, or the controlling of the properties of the coating by means of these differences in the degree of crosslinking.
Furthermore, DE 10 2004 050 747 A1 and the as yet unpublished German patent application DE P 10 2005 045228.0-44 disclose coating compositions which comprise adducts with alkoxysilane functionality. The coating compositions described therein are cured using suitable catalysts in the presence, if appropriate, of small amounts of water, to form Si—O—Si networks. One of the applications of the coating compositions is as clearcoats in OEM systems. They lead to coatings having very high scratch resistance, but are frequently in need of further improvement in terms of weathering stability and in terms of cracking. A further disadvantage is the high price of the adducts with alkoxysilane functionality, that are included in decidedly large quantities in these coating compositions.
WO01/98393, furthermore, discloses coating compositions featuring enhanced adhesion to aluminum substrates, and comprising not only a hydroxyl-containing binder and an isocyanato-containing crosslinker but also a silane oligomer (B) having at least two isocyanate groups, as an essential constituent, said oligomer (B) being the reaction product of an isocyanate-functional compound (A) with a coupling reagent (X) which contains at least one alkoxysilane-functional group and at least one group that is reactive toward isocyanate groups.
Modifying the silane oligomers (B) with surface-active components is not described in that publication. Hence, although the coatings described in WO01/98393 may have zones of increased degree of crosslinking, the lack of surface modification of at least one of the film-forming components means that these zones of increased degree of crosslinking are distributed at random across the coating as a whole, and the targeted control of the properties of the coating by means of these differences in degree of crosslinking is not possible in the case of the coatings it describes.
US 2006-0217472 A1, furthermore, discloses that the scratch resistance of polyurethane-based coatings can be improved by taking coating compositions which comprise a hydroxyl-containing binder, a crosslinker containing isocyanate groups, and a metal catalyst for the OH/NCO reaction and adding to them an amino silane, such as bis(3-propyl-trimethoxysilyl)amine, or its reaction products with isocyanates. Modifying the aminosilanes with surface-active components, however, is not described in US 2006-0217472 A1, any more than a difference in the degree of crosslinking of the coating in the near-surface layer and in the bulk.
WO 01/09260, finally, discloses coating compositions which comprise polysiloxanes (a) having at least one reactive group, compounds (b) which have at least one group reactive with the reactive groups of the polysiloxanes, and, if appropriate, particles (c), and further constituents. In the curing reaction, therefore, the polysiloxanes do not form an Si—O—Si network with the compounds (b).
This document too fails to describe a difference in degree of crosslinking of the coating in the near-surface layer and in the bulk, and the control of the properties of the coating by means of these differences in degree of crosslinking.
The problem addressed by the present invention is therefore that of providing coating compositions which allow the properties of the resulting coatings to be set in a targeted way. Advantageously it ought to be possible by means of these coating compositions to produce coatings which differ at their surface in at least one property from the properties of the coating in the underlying volume element (bulk).
The aim in particular was to provide coating compositions which lead to coatings having a high micropenetration hardness and a high scratch resistance, more particularly a high dry scratch resistance, as it is known, typically determined in the crockmeter test. At the same time these coatings ought to lead to a highly weathering-stable network. Furthermore, the coating compositions ought to meet the requirements typically imposed in the field of automotive OEM finishing. The coating compositions ought therefore in particular to exhibit good haze, i.e., no haze, good leveling, and a very good overall visual appearance. Finally the desired properties ought to be obtained as inexpensively as possible.